Offshore drilling generally employs a vertical drilling column consisting of a multitude of successive tubular sections assembled end-to-end connecting the drilling platform floating on the sea surface to the wellhead anchored at the seabed. The drilling platform is therefore subjected to the various movements of the sea, whereas the wellhead is immobile. The oscillatfons of the platform and the swivelling of the drilling column relative to its vertical theoretical position are absorbed by ball joint devices placed at the base of the drilling column.
The vertical swinging motions of the platform due to swell are absorbed by the last section of the drilling column which is made in the form of a telescopic joint which can slidably move on an end tube carried by the platform and forming the other part of the telescopic assembly.
To meet the requirements of drilling, it is necessary to provide means which enable the different members of the wellhead located at the seabed to be actuated and the energy required for these members to function to be provided. It is also indispensable to carry out measurements at the wellhead and, for this purpose, to send probes or other measuring or visualization devices to the base of the drilling column.
In order to send energy to the wellhead, control signals or measuring means, lines consisting of pipes or cables capable of transporting a hydraulic fluid or energy or electrical or acoustic signals are used. These lines associated with the drilling column consist of several successive sections and a flexible end junction part connected to the platform. Each of the sections of the lines is attached to the periphery of a section of the drilling column and comprises joining means at each of its ends. During the assembly of the drilling column, the sections of this column being attached successively to one another, the sections of the lines are also automatically joined at the time of assembling the column sections. A continuity of each of the peripheral lines between the platform and the base of the drilling column is thereby ensured.
The end parts of the lines are connected, on the platform, to different points for the supply of hydraulic fluid or of electrical energy and to other actuating or measuring means which ensure the regulation of the drilling.
At the end of the drilling column assembling operations, it is essential to ensure the connection of each of the upper sections of the lines attached to the telescopic joint, at the corresponding flexible end part connected to the platform.
For this purpose, when all the sections of the drilling column have been assembled, this operation being carried out at the platform level, and then lowered through the passage opening provided in this platform, the upper end section forming the telescopic joint assembled at the upper end of the drilling column is also lowered through the passage opening in the platform, until its upper part consisting of a supporting means comes to rest on corresponding supporting means consisting of a wedging crib attached to the platform; an operator must then carry out the joining of the end parts of the lines from a place located below the wedging crib of the platform.
This manual operation requires the operator to work from a basket suspended below the platform and consists, for this operator, after catching the muff joints of the connecting parts, in introducing these male parts into the corresponding female parts of the sections carried by the telescopic joint. It is quite obvious that this operation is complex, dangerous and cannot always be carried out under conditions which ensure that the connections are achieved satisfactorily.